1. Field of the Invention
This invention relates to an aid for the disabled, for example to a folding backrest of a wheelchair.
2. Description of the Prior Art
Folding wheelchairs are commonly carried from place to place in motor cars, so that a patient may become mobile at his destination.
It is conventional for substantially the whole, or an upper part of, the backrest of a folding wheelchair to hinge down rearwardly to decrease the overall height of the wheelchair for easy accommodation of the wheelchair in a back seat or a boot of a motor car.
For example, it is known from British Patent Specification No. 1175684 for two side frames of a folding wheelchair to include two rear upper and two rear vertical lower side tubes, with a strip of canvas or like material extending between the two upper tubes as a rest for the patient's back. The two upper tubes are connected by rear hinges to the respectively lower tubes so that they can be turned down rearwardly from raised conditions in which their lower ends extend vertically upwards from the lower tubes and their remainders extend almost vertically upwards but slightly rearwardly. The two upper tubes are releasably held in their raised positions by respective latching pins which are spring-biassed into positions in which they project as sliding fits out of the lower ends of reinforcing bushes fixed in the lower ends of the upper tubes into the upper ends of reinforcing bushes fixed in the upper ends of the lower tubes. The upper ends of the pins are bent over to project laterally out of slots along the upper tubes and are externally provided with respective knobs whereby an attendant can raise the pins out of the lower tubes against the action of the springs to allow the two upper tubes to be hinged down rearwardly.
This latching arrangement is based upon linearly sliding parts and in practice is prone to jamming. Unfortunately, the looser the fit between the sliding parts in the latched, raised position of the backrest, and thus the less prone to jamming, the greater the degree of free movement between the sliding parts and thus the greater the amount of rattling during use of the wheelchair.
U.S. Pat. No. 4,164,354 discloses similar latching mechanisms in a folding wheelchair except that, instead of the latching mechanisms being at about seat level, they are at about arm rest level.
British Patent Specification No. 1203431 discloses a latching mechanism for a linkage comprised of first and second rectangular strips to the first of which is rivetted a triangular plate at an apex of which the second strip is pivotally mounted. On the second strip is also pivotally mounted a latching device consisting of two triangular plates fixed together by two posts. The nearer end of the first strip extends between the two plates and between the two posts in the latched condition, and the latching device is urged into that position by a torsion spring acting between the device and the second strip. One of the two plates has an edge zone bent over the outer edge of the second strip to form a latch-releasing flange for pressing by a user to move the outer post from the path of the nearer end of the first strip.
This mechanism is unsuitable for use in relation to a wheelchair backrest in that the elongate members of the linkage are not end-to-end in their latched condition, and thus the canvas material of the backrest could not be both smooth in that condition and well attached to the elongate members. Moreover, the patient would be liable to catch, or even hurt, himself on the projecting nearer end of the foremost one of the members. Another disadvantage of the mechanism is that the latching device can perform a significant amount of free movement relative to the first strip in the latched condition, giving a significant rattle problem.